The present invention relates to eliminating voltage transition causing audible click noises in Class D audio power amplifier having a single power supply and more particularly to minimizing current or voltage inrush upon startup in switching power converters.
As illustrated in FIG. 1, in switching power converters 10 having a feedback loop 12 for maintaining output voltage and target output voltage other than 0V, there is a large inrush current flowing into output capacitors C1 when a switching power converter 10 is starting up. The switching power converter 10 includes a power supply 18 for providing input voltage VIN; a reference voltage supply 20; an error amplifier 22 operating on output voltage from an output node, the output voltage being provided by the feedback loop 12, and the reference voltage; an output control device 16 for controlling a high switch Q1 of a switching stage having the high switch Q1 connected to a low switch Q2 at a common node; an inductor L1 connected between the common node and the output node; and the output capacitor C1 connected between the output node and the ground. The low switch Q2 of the switching stage is illustrated as a diode.
The inrush current flow happens because of a nature of the feedback loop 12. As illustrated in FIG. 2, during an initial current transition, the control loop 12 forces an output control device 16 to output a maximum amount of current into the output capacitors C1.
One way to reduce the inrush current is to implement a current limit. However, necessity of a current sensing device which is also required for carrying rated current, makes this solution bulky and expensive.
Another way to minimize the inrush current is to implement soft start PWM. This method is difficult to implement into a control scheme with self-oscillating PWM due to modulation index limitations. For this solution the output voltage needs to be started from a certain voltage level.